Developmental and Structural Section
Guo, Jinyan , Wilson, C. .
Origins and evolutionary development of sepal crest in Iris.
The genus Iris comprises approximately 270 species. Fifty-eight of these have a morphologically diverse structure called the “crest” that is perpendicular to the lamina of the sepal, generating a three-dimensional sepal. Most crested species are within the monophyletic subgenus Scorpiris while others are in subgenera Limniris and Nepalensis. All species in subgenus Liminiris section Lophiris have a crested sepal and these Iris have been considered the crested Iris group. Molecular phylogenetic studies indicate at least six origins for the sepal crest in Iris. In this study, the structure and development of sepal crests were investigated using light and scanning electron microscopy and analyzed within a phylogenetic context. Data showed that development of the sepal crest varied both spatially and temporally. In the six lineages studied, all crests were initiated as a central ridge and divergent morphologies resulted from subsequent differences in development. Four patterns were recovered: 1) the initial developmental pathway lasts until maturity resulting in a crest that is a central ridge, 2) the central ridge is pronounced and has multicellular trichomes, 3) the central ridge is fringed distally, and 4) the distal portion of the ridge is fringed and has finger-like or laminar cellular outgrowths. Studies of mature sepals showed that developmental pathways leading to the most elaborated crests also resulted in the differentiation of vascular tissues within crests. Studies of early developmental stages of floral buds showed that outgrowth of the central ridge was initiated by an adaxial meristem and the resulting ridge occupied the space between the two anther thecae. Thus, both the packing strategy of floral buds and the genetic pathway for adaxial growth may contribute to the three dimensional structure of crested sepals.
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1 - Rancho Santa Ana Botanic Garden/Claremont Graduate University, Botany, 1500 North College Ave., Claremont, CA, 91711, USA
2 - Rancho Santa Ana Botanic Garden, 1500 N. College Ave, Claremont, California, 91711, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 551A/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 11:30 AM